The disclosed subject matter relates to techniques for hyperspectral imaging.
Spectral imaging generally involves the collection and processing of information across the electromagnetic spectrum, which can provide a more detailed representation of a scene compared to what is visible to the human eye. Different materials absorb and emit electromagnetic radiation in different manners, and this spectrum can serve as a “fingerprint” for a particular material, helping to identify it from others. The ability to visualize multiple frequencies of the spectrum can permit the material composition of an imaged region to be deduced and, with adequate post-processing, can provide detailed information about the material composition of the environment or sample. As a result, hyperspectral imagers can be used for spectroscopic identification of solids, gasses, and liquids—such as biological agents, types of polymers, exhaust fumes, and the like.
One aspect of the design of hyperspectral imaging techniques concerns how to efficiently record and transmit hyperspectral images. In general, certain approaches to hyperspectral imaging can include obtaining the intensity I(x,y,v,t) of a scene in the (x,y) plane at frequency v of an electromagnetic spectrum at a time t. In common hyperspectral imagers, a two-dimensional slice is acquired at a time. For instance, a spectrometer can be used to acquire the spectrum across a slice along the x-axis; then, this acquisition is repeated in time while scanning across the other dimension, y. Another method is to instantaneously record I(x,y,t) and then sweep over the last dimension v; however, only a single spectral component v is acquired at any given time, while the remaining spectral components are rejected, In connection with each of these general approaches, some information is lost since not all dimensions (x,y,v,t) are recorded simultaneously. Thus, in these hyperspectral imagers, only a slice in parameter space is imaged at a time, while the remaining information is rejected or lost. In another technique, a scanning interferometer is used to acquire a hyperspectral image by Fourier transform interferometery; however, this requires a complex setup with a scanning interferometer path, which can make the method slow and the apparatus complex and large.
Certain hyperspectral imaging techniques attempt to address the tradeoff between spatial and spectral resolution. For example, interferometric techniques can be used to spread the spectra onto a multiple pixels and/or the pixels can be arranged in a two-dimensional array such that some pixels record spectral information and others record spatial information. However, such techniques can still involve some concession of spectral resolution for spatial resolution, and further can be limited in acquisition rate (frame rate) because a greater number of total pixels is required. Accordingly, there is a desire for hyperspectral imaging techniques that allow for both high spatial resolution and high spectral resolution at a high frame rate, while also optimizing photon throughput (i.e., not rejecting light).